The devil is the mastermind of anything evil only by the act of him sining against God alone and sending him down on earth has cursed alot of problems for humanity and mankind with a lot of evil torments like, witch crafty attack spiritual attack, human beings has been posessed by demons.
And everything the devil possessed right from the time he was sent down on earth and all his followers that was sent down with him the world has been experiencing demonic attack, and demonic cultivation and demonic possession and demonic presence. The existence of demons in the world is from Satan because he has introduced more demons by influencing many humans and they have been multiplying through men that was possessed by the devil and through greediness and sin of man kind and also through satanic initiations, Satan has so dealed with ignorant people to the extent that they don't know when they became influenced by the devil through initiations of peer groups and without been a through child of God one is vulnerable to becoming one. Some people has gradually turned to demons but they don't know.